where is USB-C port on IMAC

If you happen to have a newer iMac, then they are on the back with all the other ports. But more likely, as P.Philips has said, you most likely have USB 3.1 USB-A ports

You also have Thunderbolt port, so it is possible to get a Thunderbolt 3-to-Thunderbolt 2 adapter from Apple, then buy a Thunderbolt 3 dock, which has USB-C ports on it. This might actually allow you to drive USB-C devices at USB 3.1 gen 2 10 gigabits/sec.

I'm sure there are USB-A-to-USB-C adapters as well. But these would be limited to USB 3.1 gen 1 and 5 gigabits/sec.

Of course the devices at the other end of the USB-C cable needs to be capable of 10 gigabits/sec, otherwise the speed does not matter.

iMac (21.5-inch, Late 2013) does not have USB-C ports - that port type only appear on newer versions of iMacs.

Suggestion - do not list serial numbers or any other personal information of the ASC Forums.

That is how I was able to trace the specific information on your computer.

If this is the Apple Magic Mouse, and it came with a USB-C to Lightening cable, just get a USB-A to Lightening cable. You can find USB-A to Lightening cables for iPhones, iPads, AirPods, etc... all over the internet.

If this is for some 3rd party mouse, figure out the connector on the mouse side, and get a cable that goes from USB-A to whatever that connector is.